HER2 inhibitors dramatically changed care for many breast cancers; however, less is known about HER3, which acts in concert with HER2. Does HER3 have the same potential to reshape treatment strategies? Erika Hamilton, MD, director of breast cancer and gynecologic cancer research at Sarah Cannon Research Institute in Nashville, talks with Bob Figlin, MD, the Steven Spielberg family chair in hematology-oncology at Cedars-Sinai Cancer Center in Los Angeles, about HER3, how it works, and how new antibody-drug conjugates (ADCs) that target HER3 are already showing activity in hard-to-treat disease. She also explains how sequencing ADC therapies may work and what other changes could be next.